This invention relates to a device for detecting the rotating speed of a fan motor, particularly to one including a motor and a gear case secured in front of the motor and having plural gears engaged with one another inside, with one of them embedded with a permanent magnet, and also having a magnetic inductive element to cooperate with the permanent magnet for operating together to detect the rotating speed of the motor.
One conventional device for detecting the rotating speed of a motor shown in FIG. 1 has an encoder functioning as a light-controlling element at the rear side of a motor (A) to detect the rotating speed of the shaft of the motor (A). Another conventional device shown in FIG. 2 has a rotating disc B1 under the center shaft B0 of a motor (B) and a permanent magnet B10 fitted around the rotating disc B1. Thus, the magnet B10 cooperates with a magnetic inductive element B2 to operate together to detect the rotating speed of the motor.
Although two conventional devices mentioned above are available for detecting the rotating speed of a motor, yet the aforesaid encoder or a magnetic inductive element has to be installed at the rear side of the motor, thus not only complicating the structure of a motor, but increasing manufacturing cost as well. Besides, the aforesaid encoder is not suitable for provided in a gear case, which is filled with machine oil, otherwise operation cannot be carried on normally.
The objective of this invention is to offer a device for detecting the rotating speed of a fan motor, possible to facilitate its installing and to take less space.
The features of the invention are described below.
1. A permanent magnet respectively having a N pole and a S pole is embedded in any one of plural gears in the gear case connected with a motor and the permanent magnets together with a magnetic inductive element (such as hall effect element) positioned above it are activated to operate together by rotating of the gear to detect the rotating speed of the motor.
2. The magnetic inductive element (HALL IC is the best) of this invention is not affected by the machine oil in the gear case, always keeping a good operating condition.